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1
HYDRODYNAMIC STUDY OF THREE
PHASE SEMI FLUIDIZED BED WITH
IRREGULAR AND HOMOGENEOUS
BINARY MIXTURES
A Project submitted to the
National Institute of Technology, Rourkela
In partial fulfilment of the requirements for
Bachelor of Technology (Chemical Engineering)
By
Bhabani Sankar Das Roll No. 10600014
&
Biswajeet Patnaik Roll No. 10600038
Under the guidance of Prof.(Dr.) G.K.Roy
DEPARTMENT OF CHEMICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
ORISSA -769 008, INDIA
2010
2
DEPARTMENT OF CHEMICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY,
ROURKELA -769 008, INDIA
CERTIFICATE
This is to certify that the thesis entitled Hydrodynamic study of Three Phase semi
Fluidized Bed with Irregular and homogeneous binary mixtures, submitted by Bhabani
Sankar Das & Biswajeet Patnaik to National Institute of Technology, Rourkela is a record
of bonafide project work under my supervision and is worthy of the partial fulfillment for the
degree of Bachelor of Technology (Chemical Engineering) of the Institute. The candidates
have fulfilled all prescribed requirements and the thesis, which is based on candidates’ own
work, has not been submitted elsewhere.
Supervisor
Prof.(Dr.) G.K.Roy Department of Chemical Engineering National Institute of Technology
Rourkela - 769008 INDIA
3
ACKNOWLEDGEMENT
It is with a feeling of great pleasure that we express our most sincere heartfelt gratitude to
Prof. (Dr.) G.K.Roy for suggesting the topic for our project and for his ready and able
guidance throughout the course of preparing this report. We are greatly indebted to him for
constructive suggestions and criticism from time to time during the progress of our work.
We thank the staff members of our department for their invaluable help and guidance. Lastly
we thank all our class mates, who have helped us in some form or the other in the completion
of our report.
BISWAJEET PATNAIK ROLL NO: -10600038
BHABANI SANKAR DAS ROLL NO:-10600014
4
ABSTRACT
Fluidization refers to a process by which a fluid like state is imparted to granular solid
particles by the passing of a fluid upwards through the bed of particles. A semi fluidized bed
is characterized by a fluidized bed and a packed bed in a series within a single contacting
vessel. Gas-liquid-solid semi fluidization is defined as an operation in which a bed of solid
particles is suspended in gas and/or liquid upward flowing media due to the net gravitational
force on the particles and the motion of the particles is restricted by a top restraint. Such an
operation generates intimate contact between the gas, liquid and solid particles in these
systems and provides substantial advantages for applications in physical, Chemical and
biochemical processing involving gas, liquid and solid phases.
The experiments were conducted using liquid as the continuous phase and gas as the
discontinuous phase. In this work air, water and dolomite (2.31mm, and 1.7mm) are used as
the gas, liquid and solid phases respectively. The experiments were carried out in a 100 mm
ID of 2m height vertical Plexiglas column.
Knowledge of minimum liquid semi fluidization velocity is essential for the successful
operation of gas- liquid-solid semi fluidized beds. Bed pressure measurements have been
made to predict the values of the minimum liquid semi fluidization velocity. In the present
work, hydrodynamic characteristics viz., the pressure drop, bed expansion of a co-current
gas- liquid-solid semi fluidized bed has been studied. These have done in order to develop a
good understanding of each of the flow regime in gas- liquid and liquid-solid semi
fluidization.
The effect of static bed height, particle size, liquid velocity and gas velocity on
hydrodynamics parameters like minimum semi fluidization velocity, pressure drop,
expansion ratio have been investigated. Experimental study based on statistical design has
been made to investigate the expansion ratio of semi fluidized bed.. The experimental values
have been compared with those predicted by the correlations and have been found to agree
well.
Keywords: Semi fluidization, packed bed formation, minimum and maximum semi
fluidization velocity, expansion ratio, factorial design.
5
CONTENTS
PAGE NO.
1. INTRODUCTION 9
2. LITERATURE REVIEW
2.1. MODES OF OPERATION 12
2.2. APPLICATIONS 14
2.3. PREVIOUS WORK 15
2.4. PRESENT WORK 16
3. EXPERIMENTAL
3.1. EXPERIMENTAL ASPECTS 18
3.2. SCOPE OF EXPERIMENT 23
3.3. EXPERIMENTAL DATA 24
3.4. RESULTS & DISCUSSIONS 26
4. DEVELOPMENT OF CORRELATIONS
4.1 HEIGHT OF PACKED BED FORMATION 38 4.2 MINIMUM LIQUID SEMI FLUIDIZATION VELOCITY 41
4.3 MAXIMUM SEMI FLUIDIZATION VELOCITY 42
5. CONCLUSIONS 45
6. REFFERENCES 47
6
LIST OF TABLES:
Table 3.2.1 Properties of Bed Materials
Table 3.2.2 Properties of Fluidizing Medium
Table 3.2.3 Properties of Manometric Fluid
Table 3.2.4 Scope of experiments
Table 3.3.1 Variation of pressure drop with liquid flow rate at constant gas flow rate
Table 3.3.2 Variation of pressure drop with gas flow rate at constant liquid flow rates
Table 3.3.3 Variation of pressure drop with liquid flow rate at constant gas flow rate
Table 3.3.4 Variation of pressure drop with gas flow rate at constant liquid flow rate
Table 3.4.1 Min. and Max. semi-fluidization velocities at constant gas and liquid flow
Table 3.4.2 Min. and Max. liquid semi-fluidization velocities at constant gas flow rates
Table 3.4.3 Min. and Max. gas semi-fluidization velocities at constant liquid flow rates
Table 3.4.4 Min. and Max. semi-fluidization velocities at constant gas and liquid flow
rates
Table 3.4.5 Min. and Max. semi-fluidization velocities at constant gas and liquid flow
rates
Table 4.1 Scope of the factors for hydrodynamics for factorial Design Analysis
Table 4.2 The effects of parameters as per factorial design analysis
Table 4.3 Comparison of experimental values of expansion ratio with that of calculated
values
Table 4.4 Scope of the factors for hydrodynamics for factorial Design Analysis
Table 4.5 The effects of parameters as per factorial design analysis
Table 4.6 The effects of parameters as per factorial design analysis
Table 4.7 Comparison of experimental values with calculated values
Table 4.8 Comparing min. liquid semi fluidization velocity for binary mixtures with that
for pure component irregular particles
7
LIST OF FIGURES:
Fig 2.1 : Modes of three phase fluidization
Fig 2.2 : Schematic representation of the Mode 1-a fluidized Bed Reactor
Fig 3.1 : A schematic diagram of the experimental set up
Fig 3.2 : A structure for perforated grid plate
Fig 3.3 : Schematic diagram of conical section
Fig 3.4.1: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.2: Variation of bed pressure drop with superficial gas velocities at different
superficial liquid velocities
Fig 3.4.3: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.4: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.5: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.6: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.7: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.8: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
Fig 3.4.9: Variation of Hpa/Hs with Ul at different Ug
Fig 3.4.10: Variation of Hpa/Hs with Ul at different Ug
Fig 3.4.11: Variation of Hpa/Hs with Ul at different Ug
Fig 3.4.12: Variation of Hpa/Hs with Ul at different Ug
Fig 3.4.13: Variation of Hpa/Hs with Ul at different Ug
Fig 3.4.14: Variation of Hpa/Hs with Ug at different Ul
Fig 3.4.15: Variation of Hpa/Hs with Ug at different Ul
Fig 3.4.16: Variation of Hpa/Hs with Ug at different Ul
Fig 3.4.17: Variation of Hpa/Hs with Ug at different Ul
8
NOMENCLATURE:
dp Particle diameter, m
Hpa Top packed bed height, m
Hs Static bed height, m
Ul Superficial liquid velocity, m/s
Ug Superficial gas velocity, m/s
Ulmsf Minimum liquid semi fluidization velocity, m/s
Ugmsf Minimum gas semi fluidization velocity, m/s
UlMsf Maximum liquid semi fluidization velocity, m/s
UgMsf Maximum gas semi fluidization velocity, m/s
R Expansion ratio
Vg Gas flow rate (lpm)
Vl Liquid flow rate (lpm)
9
CHAPTER 1
INTRODUCTION
10
A semi fluidized bed is characterized by a fluidized bed and a packed bed in a series within a
single contacting vessel. The phenomenon of semi fluidization was first reported which was
related to mass to mass transfer in a liquid solid system. A semi fluidized bed is formed when
a mass of fluidized particles is compressed by fluids with a porous retaining grid at the top.
Fixed bed or packed bed, batch and continuous fluidization and semi fluidization all are two
phase phenomena. In case of batch fluidization if the free expansion of the bed is restr icted
by the introduction of porous disc or sieve and the fluid velocity is increased the particles are
fluidized and the expansion starts with further increase in velocity of fluid the particles will
be carried and formation of a fluid bed results at the top. So by the introduction of restraint
some of the particles are distributed to the bottom section which is in the form of a packed
bed. This is known as semi fluidization which can be considered as a new type of solid fluid
contacting method which combines features of both fixed and fluidized beds. Semi
fluidization is a compromise between the two and the particles can be distributed into the two
sections as desired by choosing the parameters like position of restraint, fluid velocity etc.
The literature available so far on semi fluidization can be classified under the following heads
i) Studies oriented towards prediction of the onset and maximum semi fluidization
velocities.
ii) Studies oriented towards the prediction of packed bed height.
iii) Studies on total pressure drop.
iv) Studies on mass transfer, reaction kinetics and other related fields.
11
CHAPTER 2
LITERATURE REVIEW
12
Semi fluidization is a new and unique type of fluid-solid contacting technique which has been
reported recently. This type of technique overcomes the disadvantages of fluidized bed
namely back mixing of solids, attrition of solids and problems involving erosion of surfaces.
This also overcomes certain drawbacks of packed bed, viz. non-uniformity in temperature in
the bed, channel flow and segregation of solids. An extensive review relating to various
aspects of hydrodynamics, heat and mass transfer and special features of semi fluidized bed
reactor has been given by Murthy and Roy[1]. Semi fluidized beds can be operated either in
a two phase or three phase mode. Of late more interest has been taken in three phase mode of
operation. 2.1 MODES OF OPERATION(three phase)
Gas- liquid-solid fluidization can be classified mainly into four modes of operation. These
modes are co-current three phase fluidization with liquid as the continuous phase (mode I-a),
co-current three phase fluidization with gas as the continuous phase (mode I-b), inverse three
phase fluidization (mode II-a), fluidization represented by a turbulent contact absorber (TCA)
(mode II-b). Modes II-a and II-b are achieved with a counter-current flow of gas and liquid.
Due to complex nature of three phase fluidization, however, various methods are possib le in
evaluating the operating and design parameters for each mode of operation.
Based on the differences in flow directions of gas and liquid and in contacting patterns
between the particles and the surrounding gas and liquid, several types of operation for gas-
liquid-solid fluidizations are possible. Three phase fluidization is divided into two types
according to the relative direction of the gas and liquid flows, namely, co-current three phase
fluidization and counter-current three phase fluidization [2].
In co-current three-phase fluidization, there are two contacting modes characterized by
different hydrodynamic conditions between the solid particles and the surrounding gas and
liquid. These modes are denoted as mode I-a (figure 2.2) and mode I-b (figure 2.1). Mode I-a
defines co-current three phase fluidization with liquid as the continuous phase, while mode I-
b defines co-current three phase fluidization with gas as the continuous phase. In mode I-a
fluidization, the liquid with the gas forming discrete bubbles supports the particles. Mode I-a
is generally referred to as gas- liquid fluidization. The term bubble flow, in Epstein’s
taxonomy [9], includes two types of flow for mode I-a namely, liquid- supported solids and
bubble supported solids.
Counter-current three-phase fluidization with liquid as the continuous phase, denoted as
mode II-a in figure: 2.1, is known as inverse three-phase fluidization. Counter-current three-
phase fluidization with gas as the continuous phase, denoted as mode II-b in figure: 2.2, is
known as a turbulent contact absorber, fluidized packing absorber, mobile bed, or turbulent
13
bed contactor. In mode II-a operation the bed of particles with density lower than that of the
liquid is fluidized by a downward liquid flow, opposite to the net buoyant force on the
particles, while the gas introduced counter currently to that liquid forming discrete bubbles in
the bed.
Fig 2.1: Modes of three phase fluidization
Fig 2.2 : Schematic representation of the Mode 1-a fluidized Bed Reactor
14
2.2 APPLICATIONS(two phase and three phase semi fluidized beds)
Gas liquid solid fluidized bed had emerged in recent years as one of the most promising
devices for 3 phase operations. Such devices are of considerable industrial importance as
evidenced by their wide use in chemical, petrochemical and b io-chemical processing.
The application of gas liquid solid fluidized bed system to bio-technological processes
such as fermentation and aerobic waste water treatment has gained considerable
importance in recent years.
Application of semi fluidization in the fields of reaction kinetics has already been
initiated. This technique is advantageous for fast exothermic reactions such as vapor
phase oxidation and chlorination of hydrocarbons etc.
Use of this technique in studies in mass transfer have shown that the magnitude of mass
transfer coefficient can be controlled approx. linearly and within the limits of a
completely fixed bed and completely fluidized bed by means of expansion alone.
The application of semi fluidized beds has been broadly stressed by Fan and Hsu.
According to them semi fluidized beds find wide applications as reactors for exothermic
reactors and bioreactors in ion exchange and in filtration operation for the removal of
suspended particles from gases and liquids.
It is also widely used in industrial applications like drying, adsorption, reaction kinetics,
solid catalyzed reactions, heat transfer etc.
2.3 PREVIOUS WORK
Little information is available on semi fluidization. Previous work relating to hydrodynamics
study of two phase semi fluidized beds include that of Biswal et.al[6], Ho et.al[7] and Roy
and Murthy[1].Jena et.al[4],[5],[8],[10] had carried out investigations relating to some
hydrodynamic aspects like bed expansion, pressure drop, minimum and maximum liquid
semi fluidization velocities for irregular, regular and cylindrical mono size particles in case of
three phase semi fluidization.
While a few information are available on the two phase semi fluidization of binary mixtures
and three phase semi fluidization of pure components, investigations relating to
hydrodynamics of three phase fluidization of binary mixtures are almost absent. Therefore in
present study hydrodynamic investigations viz. the pressure drop, minimum and maximum
semi-fluidization velocity and rate of top packed bed formation in a co-current gas- liquid-
solid three phase semi fluidized bed with binary homogeneous mixture using liquid as the
continuous phase and gas as the discontinuous phase have been taken up.
15
2.4 PRESENT WORK
Fluidized bed and semi fluidized bed units are found in many plant operations in chemical,
pharmaceutical, and mineral industries. Despite their widespread applications, much of the
development and design of fluidized bed reactors have been empirical as the complex flow
behaviors of gas-solid flow in these systems makes flow modelling a challenging task. The
fundamental problem encountered in modelling hydrodynamics of fluidized bed is the motion
of the two phases of which the interface is unknown and transient, and the interaction is
understood only for a limited range of conditions.
The process engineer must have a good understanding of the factors that affect the behavio ur
of semi fluidized beds in order to use them effectively. Therefore, it is crucial that (s) he be
able to predict how pressure drop will change under different fluidization and semi-
fluidization conditions. The main concepts to be studied are the minimum semi fluidization
velocity required for the bed of particles and the degree of pressure drop that the upward
flowing fluid experiences. By being able to predict these properties, the engineer is able to
design processes for industrial applications and find the best conditions to run the apparatus.
The main objectives of this work are
To determine the minimum liquid semi fluidization velocity, the bed pressure
measurement has been done.
Hydrodynamics characteristics especially the pressure drop of a co-current gas- liquid-
solid semi fluidized bed have determined. For this the experimental work has performed.
Also the effect of bed expansion with the static bed height and particle size is to be
studied.
The height of top packed bed formation is to be observed for calculating maximum semi
fluidization velocity.
These have been done in order to develop a good understanding of each flow regime
in gas- liquid and liquid-solid semi fluidization.
16
CHAPTER 3
EXPERIMENTAL
17
3.1 EXPERIMENTAL SET UP: A schematic diagram of the experimental set up is shown in the Figure 3.1.The vertical
Plexiglas fluidizer column is of 100 mm ID with a maximum height of 2m.The column
consists of three sections, viz., the gas- liquid disengagement section, test section, and gas-
liquid distributor section. Water and air is used as the liquid and gas phases respectively.
1.Gas-Liquid Disengagement Section
Gas-Liquid Disengagement Section is at the top of the column, which allows gas to
escape and liquid to be circulated. Any entrained particles retain on the screen attached to the
top of this section.
2. Test Section
The test/study section is in between the gas- liquid disengagement section and gas-
liquid distributor Section. The gas- liquid flow is co-current and upwards. The whole test is
performed in this section. All the pressure taps are connected to this section.
3. Gas-Liquid Distributor Section
The gas- liquid distributor is located at the bottom of the test section and is designed
in such a manner that uniform distribution of the liquid and gas can be maintained in the
column Liquid and gas inlets are connected to this section. This is an important component of
the setup. It is a perforated plate made of G.I. sheet of I mm thick, 120 mm diameter. About
278 numbers of 2, 2.5 and 3mm pores are randomly placed in the sheet (Figure: 3.2). A
screen is placed just above the sheet to avoid the flow of bed materials in to the calming
section. Two numbers of gaskets of 3mm thick and 150mm dia. are provided between the
flange and the screen. The distribution is on integral part of calming section where it is
followed by a conical section (Figure: 3.3).The height of perpex conical section is 12 cm.
There is a gas distributor consists of 50 numbers of 2 and 3mm pores placed randomly. In this
section the gas and liquid streams merged and passed through the perforated grid. The mixing
section and grid ensure that the gas and liquid are well mixed and evenly distributed into the
bed.
18
4. Pressure Taps
The column is equipped with twenty one pressure taps. Three taps each in gas-liquid
disengagement section and Gas- liquid distributor Section, fifteen in test section. These are
installed at equal intervals of 30 cm and connected to the manometers.
5. Rotameter
There are one lower range (0-10 lpm) and two higher range (0-100, 0-200lpm)
calibrated rotameter for measurement of liquid and gas flow rates.
6. Air Compressor
It is a multistage compressor (3 Phase, 1 HP, 1440rpm). It consists of a receiver,
which receives compressed air from the compressor and an air accumulator/constant pressure
tank. The tank is a horizontal cylinder used for storing the compressed air. The purpose of air
accumulator/ constant pressure tank is to dampen any pressure fluctuation. The silica gel
tower absorbs the moisture carried out by the air from the air accumulator. The moisture and
oil free compressed air is fed to the fluidizer through the calibrated rotameter.
7. Liquid Pump
A centrifugal pump (Single phase, 1HP, and 2900rpm) is used for delivering liquid to
the fluidizer through the calibrated rotameter.
8. Liquid Reservoir
There is a liquid reservoir (42X32X70cm3) installed at the base of the column. The
main purpose of this liquid reservoir is to store the bypass and recycled liquid.
19
Fig 3.1 A schematic diagram of the experimental set up
20
Fig 3.2 A structure for perforated grid plate
Fig 3.3 Schematic diagram of conical section
Oil free Compressed
Air
Water
Gas distributor
Gasket
Liquid-gas distributor
Screen
21
3.1.2 EXPERIMENTAL PROCEDURE
The three phases present in the column were 1.7 and 2.31 mm dolomite, tap water and the oil
free compressed air. The air-water flow were co-current and upwards. Accurately weighed
amount of material was fed into the column and adjusted for a specified initial static bed
height. Water was pumped to the fluidizer at a desired flow rate. Then air was injected into
the column through the air distributor. Approximately five minutes was allowed to make sure
that the steady state was reached. Then the readings of each manometer were taken. Also, the
bed expansion was noted. The values of minimum semi fluidization velocity for every run
have been obtained by plotting pressure drop across the beds versus liquid flow rates at
constant air flow rates. Maximum semi fluidization velocity is predicted from the
extrapolation of the plot of Hpa/Hs.
PRECAUTIONS
Care should be taken in using the vents otherwise there may be the chance of air
bubbles in the manometer tubes, which will affect the readings.
There should be no leakage in the pipe lines.
There should be no fluctuations in water and air flow rates. The temperature of water
should be kept at constant by exchanging with cold water. So at each set of readings
the temperature should be noted.
The maximum and minimum bed height should be taken correctly.
For every break if the original levels in manometers have not seen, then make the
level by adjusting the vents.
22
3.2 SCOPE OF EXPERIMENTS AND PROPERTIES OF MATERIALS
3.2.1 Properties of Bed Materials
Sl. No. Materials Mesh size dp,mm p (kg.m-3)
01 dolomite -6+7 2.31 2,652
02 dolomite -7+8 1.7 2,652
3.2.2 Properties of Fluidizing Medium
Medium (kg.m-3) (Ns/m2)
Air at 250C 1.168 0.00187
Water at 250C 1,000 0.095
3.2.3 Properties of Manometric Fluid
(gm/cc) (Ns/m2)
Mercury 13.6 0.15
3.2.4 Scope of experiments
Static bed height(cm),Hs
10
15
20
25
Mixture composition
50:50
60:40
70:30
80:20
Mean diameter(cm)
0.179
0.185
0.19
0.195
Expansion Ratio,R
2
3
3.5
4
23
3.3 EXPERIMENTAL DATA
For Hs=10cm and R=3 and 50:50 mixture of material
Table 3.3.1 :Variation of pressure drop with liquid flow rate at constant gas flow rate
Liquid
velocity
(m/s)
Gas velocity (m/s)
0.006 0.0106 0.0148 0.0212
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
0.004246 3.708 0 6.18 0 7.42 0 7.42 0
0.012739 4.944 0 6.79 0 8.65 0 8.03 0
0.021231 5.562 0 7.41 0 9.27 0 8.65 0
0.033970 5.562 0 7.41 0 9.88 0 8.65 0
0.047710 5.562 0 7.41 0 9.88 0 8.65 0
0.053079 5.933 0.4 7.66 0.2 9.88 0 9.27 0.8
0.063694 6.180 1.0 8.03 0.8 10.13 0.5 9.88 1.0
0.084926 6.427 1.8 8.65 2.0 10.51 2.0 10.50 2.5
0.106517 6.551 3.0 9.27 4.0 11.12 4.0 11.12 5.0
Table 3.3.2: Variation of pressure drop with gas flow rate at constant liquid flow rates
Gas
velocity
(m/s)
Liquid velocity (m/s)
0.0424 0.0636 0.0743 0.0848
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
0.0089 4.939 0 6.790 0 7.16 0 7.400 0
0.0106 5.556 0 6.910 0 7.65 0 7.400 0
0.0148 5.927 0 7.160 0 8.02 0 7.400 0
0.0212 6.174 0 7.408 0 8.02 0 9.631 2
0.0318 6.174 0 7.408 0 8.02 0 9.878 3
0.0424 6.421 0.5 8.020 0.5 8.30 0.8 10.490 4
0.0531 7.038 1.0 8.640 1 8.64 1.5
0.0637 8.396 2.0 9.014 2 9.014 2.5
24
For Hs=15cm and R=2 and 50:50 mixture of material
Table 3.3.3 : Variation of pressure drop with liquid flow rate at constant gas flow rate
Liquid
velocity
(m/s)
Gas velocity (m/s)
0.0106 0.0148 0.0212 0.0318
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
0.004200 2.470 0 2.47 0 2.47 0 2.470 0
0.021231 3.708 0 4.32 0 4.32 0 4.326 0
0.042463 4.944 0 5.19 0 5.19 0 5.560 0
0.063694 6.180 0 6.79 0 6.79 0 7.040 0
0.074310 6.180 0 6.79 0 6.79 0 7.040 0
0.084926 6.180 2 6.79 0 6.79 0 7.040 0
0.095541 6.550 5 7.41 7 7.41 5 7.300 8
0.106157 6.790 8 8.03 9 8.03 8 8.030 10
0.122801 7.410 10 8.13 11 8.23 11.2 8.330 12
Table 3.3.4: Variation of pressure drop with gas flow rate at constant liquid flow rate
Gas
velocity
(m/s)
Liquid velocity (m/s)
0.0424 0.0636 0.0848 0.1060
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
Pressure
drop
(KPa)
Hpa
(cm)
0.0089 2.47 0 2.47 0 2.47 0 3.09 0
0.0106 2.84 0 3.09 0 2.82 0 3.58 0
0.0148 3.09 0 3.46 0 3.09 0 3.71 0
0.0212 3.46 0 3.71 0 3.46 0 3.71 0
0.0318 3.46 0 3.71 0 3.46 0 3.955 4
0.0424 3.58 3 3.83 4 3.58 3 4.69 6
0.0531 3.7 5 4.33 6 3.71 5 5.56 10
0.0637 4.32 6.5 4.69 8 4.32 6.5 6.78 12
Similar procedure is repeated for expansion ratios of 3, 3.5, 4 and for different static bed heights of 20cm, 25cm.
25
3.4 RESULTS AND DISCUSSION
Pressure drop and minimum semi fluidization velocity:
The minimum semi fluidization velocity is defined as the fluid velocity at which top of the
fluidized bed just touches the top restraint. The plot of superficial liquid velocity against
pressure drop gives a break which corresponds to minimum liquid semi fluidization velocity.
For static bed height of 15 cm and 50:50 mixture and expansion ratio R=2
Fig 3.4.1: Variation of bed pressure drop with superficial liquid velocity at different superficial gas velocities
Fig 3.4.2: Variation of bed pressure drop with superficial gas velocities at different superficial liquid velocities
26
For static bed height of 15 cm and 50:50 mixture (For expansion ratio R=2)
Fig 3.4.3: Variation of bed pressure drop with superficial liquid velocity at different superficial gas velocities
(For expansion ratio R=3)
Fig 3.4.4: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
27
(For expansion ratio R=3.5)
Fig 3.4.5: Variation of bed pressure drop with superficial liquid velocity at different superficial gas velocities
(For expansion ratio R=4)
Fig 3.4.6: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
28
For static bed height of 20 cm and For expansion ratio R=3
Fig 3.4.7: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
For static bed height of 25 cm and for expansion ratio R=3
Fig 3.4.8: Variation of bed pressure drop with superficial liquid velocity at different
superficial gas velocities
The hydrodynamic study of the three phase semi fluidized bed with irregular particles reveals
that the minimum liquid semi fluidization velocity decreases with gas velocity and pressure
drop is found to increase with superficial gas velocity for a fixed liquid superficial velocity.
29
Height of top packed bed and maximum liquid semi fluidization velocity:
Due to arrest of the free expansion of the fluidized bed by top retaining grid a packed bed is
formed at the top. In two phase system there exists a clear zone in between top packed bed
and bottom fluidized bed which almost devoid of particles. This phenomenon is not observed
in three phase fluidization, but the concentration of the particles remains low in this region.
This is due to discontinuous motion of the gas bubbles in the bed. The rate of formation of
packed bed is expressed as the ratio of packed bed height (Hpa) to the initial static bed
height(Hs). The liquid velocity at which all the solid particles are supported by fluid in top
packed bed at a constant gas velocity is called maximum liquid semi fluidization veloc ity,
which can be obtained by extrapolation of the plot of Hpa/Hs to the value of 1.
Fig 3.4.9: Variation of Hpa/Hs with Ul at different Ug
30
Fig 3.4.10: Variation of Hpa/ Hs with Ug at different Ul (For expansion ratio R=2)
Fig 3.4.11: Variation of Hpa/Hs with Ul at different Ug
(For expansion ratio R=3)
Fig 3.4.12: Variation of Hpa/Hs with Ul at different Ug
(For expansion ratio R=3.5)
31
Fig 3.4.13: Variation of Hpa/Hs with Ul at different Ug
(For expansion ratio R=2)
Fig 3.4.14: Variation of Hpa/Hs with Ug at different Ul
(For expansion ratio R=3.5)
Fig 3.4.15: Variation of Hpa/Hs with Ug at different Ul
32
(For expansion ratio R=4)
Fig 3.4.16: Variation of Hpa/Hs with Ug at different Ul
Fig 3.4.17: Variation of Hpa/Hs with Ug at different Ul
Hpa/Hs increases with gas and liquid superficial velocity. The maximum liquid semi
fluidization velocity decreases with gas superficial velocity.
For static bed height 10cm and expansion ratio R=2 and 50:50 mixture
Table 3.4.1: Min. and Max. semi-fluidization velocities at constant gas and liquid flow rates
For constant gas flow rate For constant liquid flow rate
Ug(m/s) Ulmsf (m/s)
(From
Plot3.1)
UlMsf (m/s)
(From
Plot3.3)
Ul(m/s)
Ugmsf(m/s)
(From Plot3.2)
UgMsf(m/s)
(From Plot3.2)
0.006 0.08 0.18 0.0424 0.042 0.12
0.0106 0.07 0.17 0.0636 0.035 0.11
0.0148 0.06 0.14 0.0743 0.03 0.09
0.0212 0.04 0.12 0.0848 0.0185 0.08
33
For static bed height 15cm and for 50:50 mixture for different expansion ratios
Table 3.4.2: Min. and Max. liquid semi-fluidization velocities at constant gas flow rates
Ug(m/s)
R=2 R=3 R=3.5 R=4
Ulmsf
(m/s)
UlMsf
(m/s)
Ulmsf
(m/s)
UlMsf
(m/s)
Ulmsf
(m/s)
UlMsf
(m/s)
Ulmsf
(m/s)
UlMsf
(m/s)
0.0106 0.044 0.18 0.048 0.19 0.050 0.20 0.055 0.20
0.0148 0.040 0.17 0.041 0.18 0.042 0.19 0.050 0.18
0.0212 0.035 0.16 0.038 0.16 0.040 0.17 0.045 0.17
0.0348 0.029 0.15 0.030 0.15 0.038 0.16 0.040 0.16
Table 3.4.3: Min. and Max. gas semi-fluidization velocities at constant liquid flow rates
For static bed height 20cm and expansion ratio R=3 and 50:50 mixture
Ul(m/s)
R=2 R=3 R=3.5 R=4
Ugmsf
(m/s)
UgMsf
(m/s)
Ugmsf
(m/s)
UgMsf
(m/s)
Ugmsf
(m/s)
UgMsf
(m/s)
Ugmsf
(m/s)
UgMsf
(m/s)
0.0424 0.048 0.080 0.050 0.085 0.050 0.088 0.055 0.090
0.0636 0.045 0.075 0.045 0.078 0.048 0.080 0.050 0.080
0.0848 0.042 0.068 0.043 0.070 0.045 0.072 0.045 0.075
0.1060 0.040 0.065 0.042 0.065 0.043 0.068 0.040 0.070
34
Table 3.4.4: Min. and Max. semi-fluidization velocities at constant gas and liquid flow rates
For constant gas flow rate For constant liquid flow rate
Ug(m/s) Ulmsf (m/s)
UlMsf (m/s)
Ul(m/s)
Ugmsf(m/s)
UgMsf(m/s)
0.0106 0.050 0.20 0.0424 0.050 0.088
0.0148 0.042 0.19 0.0636 0.048 0.080
0.0212 0.040 0.17 0.0848 0.045 0.072
0.0348 0.038 0.16 0.1060 0.043 0.068
For static bed height 25cm and expansion ratio R=3 and 50:50 mixture
Table 3.4.5 : Min. and Max. semi-fluidization velocities at constant gas and liquid flow
rates
For constant gas flow rate For constant liquid flow rate
Ug(m/s) Ulmsf (m/s)
UlMsf (m/s)
Ul(m/s)
Ugmsf(m/s)
UgMsf(m/s)
0.0106 0.048 0.200 0.0424 0.050 0.085
0.0148 0.044 0.170 0.0636 0.045 0.080
0.0212 0.041 0.165 0.0848 0.042 0.075
0.0348 0.039 0.150 0.1060 0.040 0.070
35
CHAPTER 4
DEVELOPMENT OF CORRELATIONs
36
4.1 HEIGHT OF PACKED BED FORMATION
The method of experimentation is based on factorial design analysis [3] and dimensional
analysis in order to bring out the effect of variables on the response The scope of the factors
consider for factorial experimentation are listed in table 4.1.1. The variables which affect the
height of the top packed bed are initial static bed height, superficial gas velocity and
superficial liquid velocity.
Table 4.1 (Scope of the factors for hydrodynamics for factorial Design Analysis)
Sl
no.
variables
General symbol
Factorial
design symbol
Minimum level(-1)
Maximum level(+1)
Magnitude of variables
1 Static bed height(cm)
Hs A 10 25 10,15,20,25
2 Gas flow rate(lpm)
Vg B 20 30 20,25,30
3 Liquid flow
rate(lpm)
Vl C 20 50 20,30,40,50
The model equations are assumed to be linear and the equations take the general form,
Y= (b0+b1A+b2B+b3C+…+b12AB+b13AC+…+b123ABC) ………………………
(4.1)
I) Coefficients are calculated by the Yates technique:
bi= Σ (αiYi)/N
II) Calculations of the level of variables:
A: Level for static bed height= (Static bed height – 17.5)/7.5
B: Level for gas flow rate = (gas flow rate - 25)/5
C: Level for liquid flow rate = (liquid flow rate – 35)/15
37
Table: 4.2 (The effects of parameters as per factorial design analysis)
Sl. No.
Treatment Combination
Experimental data
1
2
3
Effect (3)/4
Sum of squares (3)2/8
1 1 0.520 0.532 1.396 3.646
2 a 0.012 0.864 2.250 2.450 0.6125 0.75000
3 b 0.680 0.980 1.004 -0.622 0.1550 0.04800
4 ab 0.184 1.270 1.450 0.202 0.0505 0.00500
5 c 0.900 0.508 -0.332 -0.854 -.2130 0.09100
6 ac 0.080 0.496 -0.290 -0.446 0.1150 0.02500
7 bc 0.950 0.820 0.012 -0.042 0.0105 0.00020
8 abc 0.320 0.630 0.190 -0.178 -0.0440 0.00396
The following equation has been obtained:
Y= 0.456+ 0.306*A- 0.078*B+ 0.025*A*B- 0.1067*C- 0.0557*A*C- 0.0053*B*C- 0.0223*A*B*C ----------------------------------------(4.2)
The value of the coefficients indicates the magnitude of the effect of the variables and the
sign of the coefficient gives the direction of the effect of the variable. That is a positive
coefficient indicating an increasing in the value of the responses with increase in the value of
the variable and a negative coefficient showing that the response decreases with increase in
the value of the variable.
Equation developed by dimensional analysis:
=0.888* * * * * ------------(4.3)
38
Table: 4.3 :Comparison of experimental values of top packed bed formation with that of the
calculated ones (equation 4.2 and 4.3)
Static
bed
height
(cm)
Gas
flow
rate(lpm)
Liquid
flow
rate(lpm)
dp(cm)
R
Hpa/Hs
(exp)
Hpa/Hs
(cal)
(eq 4.2)
Hpa/Hs
(cal)
(eq 4.3)
%
Dev.
(eq 4.2)
%
Dev.
(eq 4.3)
10 20 20 0.179 2 0.50 0.3210 0.325 24 23
15 20 20 0.185 2 0.52 0.5306 0.510 1.9 1.9
20 20 20 0.190 2 0.80 0.7402 0.770 8.0 3.0
25 20 20 0.195 2 0.90 0.9480 0.880 5.0 2.0
10 25 30 0.179 3 0.18 0.1670 0.170 7.0 5.0
15 25 30 0.185 3 0.32 0.3840 0.353 16 9.0
20 25 30 0.190 3 0.68 0.5990 0.650 13 4.0
25 25 30 0.195 3 0.88 0.8160 0.830 7.0 6.0
10 30 40 0.179 3.5 0.04 0.0350 0.048 14 16
15 30 40 0.185 3.5 0.32 0.2390 0.300 33 6.0
20 30 40 0.190 3.5 0.48 0.4420 0.420 8.0 14
25 30 40 0.195 3.5 0.68 0.6450 0.660 5.0 3.0
10 30 50 0.179 4 0.0121 0.0130 0.0123 6.9 1.6
15 30 50 0.185 4 0.18 0.1810 0.177 0.5 1.7
20 30 50 0.190 4 0.32 0.3500 0.330 8.0 3.0
25 30 50 0.195 4 0.56 0.5190 0.530 7.0 5.0
4.2 MINIMUM LIQUID SEMI FLUIDIZATION VELOCITY
Table 4.4 (Scope of the factors for hydrodynamics for factorial Design Analysis)
Sl no.
variables
General symbol
Factorial design
symbol
Minimum level(-1)
Maximum level(+1)
Magnitude of variables
1 Particle diameter(cm)
dp
A
0.179
0.195
0.179,0.185,0.19,0.195
2 Expansion ratio
R
B
2
4
2,3,3.5,4
3 Gas flow
rate(lpm)
Vg
C
5
15
5,7,10,15
39
The model equations are assumed to be linear and the equations take the general form:
Y= (b0+b1A+b2B+b3C+…+b12AB+b13AC+…+b123ABC)
I) Coefficients are calculated by the Yates technique: bi= Σ (αiYi)/N)
II) Calculations of the level of variables: A = (dp – 0.187)/0.008;
B = (R – 3.125)/1.125; C = (Ug – 9.25)/4.25
Table 4.5 (The effects of parameters as per factorial design analysis)
Sl. No.
Treatment Combination
Experimental data
1
2
3
Effect (3)/4
Sum of squares
(3)2/8
1 1 4.0 8.4 18.9 32
2 a 4.4 10.5 13.1 -1.6 -0.4 0.320
3 b 5.0 5.4 -0.9 -4.4 -1.1 2.420
4 ab 5.5 7.7 -0.7 0 0 0
5 c 2.5 -0.4 -2.1 5.8 1.45 4.200
6 ac 2.9 -0.5 -2.3 -0.2 -0.05 0.005
7 bc 3.7 -0.4 0.1 0.2 0.05 0.005
8 abc 4.0 -0.3 -0.1 0.2 0.05 0.005
The following equation has been obtained:
Y=4-0.2*A-0.55B+0.725C-0.025AC+0.025BC+0.025ABC---------------------------(4.4)
4.3 MAXIMUM SEMI FLUIDIZATION VELOCITY
Table 4.6 (The effects of parameters as per factorial design analysis)
Sl. No.
Treatment
Combination
Experimental
data
1
2
3
Effect (3)/4
Sum of squares
(3)2/8
1 1 17 35 74 134
2 a 18 39 60 -4 -1.0 2.0
3 b 19 29 -2 -6 -1.5 4.5
4 ab 20 31 -2 0 0 0
5 c 14 -1 -4 14 3.5 24.5
6 ac 15 -1 -2 0 0 0
7 bc 15 -1 0 -2 -0.05 1
8 abc 16 -1 0 0 0 0
40
The following equation has been developed:
Y=16.75-0.5A-0.75B+1.75C-0.25BC ---------------------------------------------------(4.4)
Table 4.7 (Comparison of experimental values with calculated values)
dp(cm) R Vg(lpm) Ulmsf
(exp)
Ulmsf
(cal)
%dev UlMsf
(exp)
UlMsf
(cal)
%dev
0.179 2 5 4.0 4.00 0 17.0. 16.00 6.0
0.185 2 5 3.6 3.80 5.20 16.0 15.62 2.4
0.190 2 5 3.7 3.79 2.30 15.5 15.31 1.2
0.195 2 5 3.9 3.70 5.40 15.6 15.00 4.0
0.179 3 7 4.4 3.86 13.0 16.5 16.39 0.67
0.185 3 7 3.8 3.72 2.00 16.2 16.00 1.25
0.190 3 7 3.7 3.61 2.40 16.0 15.70 1.9
0.195 3 7 3.6 3.49 3.15 15.5 15.39 0.7
0.179 3.5 10 4.3 4.14 3.80 17.0 17.29 1.6
0.185 3.5 10 4.2 3.99 5.20 17.2 16.90 1.7
0.190 3.5 10 3.9 3.86 1.03 17.0 16.60 2.4
0.195 3.5 10 3.8 3.74 1.60 16.6 16.29 1.9
0.179 4 15 5.0 4.78 4.60 18.0 18.77 4.1
0.185 4 15 4.7 4.63 1.50 18.2 18.39 1.03
0.190 4 15 4.6 4.50 2.20 18.1 18.08 0.11
0.195 4 15 5.5 5.20 7.00 17.5 17.77 1.5
41
Table 4.8 Comparing min. liquid semi fluidization velocity for binary mixtures with that for
pure component irregular particles
Ulmsf =0.3832* * * [4]
dp(cm) R Vg(lpm) Ulmsf (binary
mix)
Ulmsf(pure
component)
0.179 2 5 4.0 9.20
0.185 2 5 3.6 9.30
0.190 2 5 3.7 9.50
0.195 2 5 3.9 9.60
0.179 3 7 4.4 10.0
0.185 3 7 3.8 10.2
0.190 3 7 3.7 10.3
0.195 3 7 3.6 10.4
0.179 3.5 10 4.3 9.83
0.185 3.5 10 4.2 9.97
0.190 3.5 10 3.9 10.09
0.195 3.5 10 3.8 10.2
0.179 4 15 5.0 9.42
0.185 4 15 4.7 9.56
0.190 4 15 4.6 9.67
0.195 4 15 5.5 9.78
42
CHAPTER 5
CONCLUSIONS
43
Three phase semi fluidization has potential application in chemical and bio –chemical
reactors and in waste water treatment reactor. For designing such systems, hydrodynamic
parameters should be known. In that direction present work will be useful. The important
hydrodynamic parameters like minimum and maximum semi fluidization velocity and packed
bed formation have been quantified by developing different correlations with the help of
experimental data. The values calculated from these correlations also compare fairly well
with the experimental values. Further it has been observed that use of the correlations
developed earlier for single component systems for the prediction of such hydrodynamic
parameters is not feasible due to high values of deviation. Therefore, the developed
correlation can be used while dealing with binary irregular mixtures. The present correlations
can be used with fair accuracy for the design of three phase semi fluidized beds systems
handling irregular binaries within the range of the variables studied.
44
REFERENCES:
[1]. J. S. N. Murthy and G. K. Roy (1986) “Semi- fluidization: a Review”, Indian Chemical
Engineer, Vol. XXIX, No.2, 9-22.
[2]. Dhanuka, V.R., and J.B. Stepanek, “Gas and Liquid Hold-up and Pressure drop
Measurements in a Three-Phase Fluidized Bed”, Fluidization Cambridge University Press,
(1978), 179-183.
[3]. Davies, O.L., “Design and Analysis of Industrial Experiments”, Longman Publishers,
(1978).
[4] H. M. Jena, G. K. Roy and B. C. Meikap, “Hydrodynamics of a Three-phase Semi-
fluidized Bed with Irregular Particles” Indian chemical engineer(2007).
[5] Simon, Thakur, Moghekar, Jena, “Prediction of pressure drop and top packed bed heights
in 3 phase semi fluidized bed with cylindrical particles” student chemical engineering
congres(2006).
[6] K.C.Biswal, S.N.Sahoo, Murthy, G.K.Roy (1990) “Dynamics of gas solid semi
fluidization of binary homogeneous and heterogeneous mixtures.”, chemical engineering
journal, Vol.70.
[7] T. C. Ho, S. J. Yau and J. R. Hopper(1987) “Hydrodynamics of semi fluidization in gas-
solid systems” department of chemical engineering, lamar university, 25-34.
[8] H. M. Jena, G. K. Roy and B. C. Meikap, “Experimental hydrodynamic study of three
phase semi fluidized bed”, Indian chemical engineering congress(2006).
[9] Epstein, N., “Three-Phase Fluidization: Some knowledge Gaps”, Can.J.Chem.Eng.
Vol.59, (1981), 649-757.
[10] H. M. Jena, G. K. Roy, K.C.Biswal, “Bed expansion behavior of cylindrical particles in
a 3 phase fluidized bed”, department of chemical engineering (2008).
Recommended